Older people with high waist-hip ratios (WHRs) have
a higher mortality risk than those with a high body mass index, or
BMI, a new study reveals.
Whereas justifiable attention is given to the increasing problem of
obesity in the general population, far less is known about the relationship
between obesity and mortality in older people, or how mortality risk
should be estimated. The excess health risks associated with having
a high BMI are known to decline with age, yet expert bodies such as
the National Institutes of Health and the World Health Organisation
have continued to use in older people the same BMI criteria as for
other age groups.
Today's study, published in the American Journal of Clinical Nutrition,
was carried out by a team based at the London School of Hygiene & Tropical
Medicine. It sought to investigate the association of BMI, waist circumference
(WC) and WHR with mortality and cause-specific mortality. The researchers
studied 14,833 patients aged over 75 from 53 family practices in the
UK; the subjects underwent a health assessment that included taking
body measurements and a follow-up (with a median of 5.9 years) for
mortality.
The findings confirmed that the current guidelines for BMI-based risk
categories overestimate the risks of excess weight in people aged over
75 and are inappropriate for older men and women. This concurs with
a previous study that found BMIs of 25-27 not to be a risk factor for
all-cause and cardiovascular mortality in those aged 65 and overą.
Most consistently, the data highlighted the risk of having a low BMI,
with people in the lowest quintile (less than 23 in men and less than
22.3 in women) demonstrating the highest risk of death for total mortality
and for major causes of death. Very underweight men (those with a BMI
of under 18.5) were found to be particularly at risk.
'An explanation for the lack of a positive association with BMI and
mortality at older ages is that, in older persons, BMI is a poor measure
of body fat', say the authors. 'The measurement of weight does not
differentiate between fat and fat-free mass, and fat-free mass (especially
muscle) is progressively lost with increasing age
Waist circumference (WC) has been proposed as an alternate or additional
measure of obesity. The study found no association with waist circumference
and mortality. The authors continue: 'A limitation of WC alone as a
measure is that it takes no account of body composition, whereas WHR
is a measure of body shape and to some extent of lower trunk adiposity
[abdominal fat]. Although it is possible theoretically for high WHR
to coexist with thinness, our data show that those with high WHR had
higher-than-average waist and average hip circumferences. We conclude
that the association observed for WHR and mortality is probably explained
by abdominal adiposity'.
The authors recommend that the current BMI-based health risk categories
to define the burden of disease related to adult overweight and obesity
be reviewed, as they are not appropriate for those over 75. They suggest
that WHR should instead be used in this age group because of its positive
relation with risk of death, and that attention should also be paid
to the problem of underweight in old age.
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on 8 August 2006 and may have been edited (e.g. in style, length, and/or
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